Accroding to the transcriptome of the 3rd instar larva of Lymantria dispar(L. dispar), a Glutathione S–transferase gene was determined and obtained, which named LdGSTe1. The open reading frame (ORF) of LdGSTe1 was 651 bp encoding a protein of 216 amino acid residues. Sequence analysis showed that the amino acid sequences of LdGSTe1 protein contained two conserved domains, namely GST_C_Delta_Epsilon and GST_N_Delta_Epsilon, belonging to the thioredoxin-like superfamily and glutathione S–transferase superfamily. Phylogenetic tree analysis indicated that the LdGST belonged to GST Epsilon family. Protein structure showed LdGSTe1 contains an N-terminal and C-terminal, and organized mainly into α–helix and β–sheet. The expression of LdGSTe1 in 3rd instar larvae L. Dispar under 4.0, 10.0 mg/L rotenone treatment was investigated using real-time fluorescence quantitative PCR. The results showed that the expression of LdGSTe1 in L. dispar was first down-regulated and then up-regulated. Therefore, LdGSTe1 gene was speculated to participate in the detoxification response of L. dispar.